Don't return any format if containsModuleSyntax throws

Author: GeoffreyBooth

lib/internal/modules/esm/get_format.js

@@ -92,7 +92,7 @@ function detectModuleFormat(source, url) {
     return containsModuleSyntax(source, fileURLToPath(url), url) ? 'module' : 'commonjs';
   } catch {
     // containsModuleSyntax throws if source is undefined and the passed filename cannot be read
-    return 'commonjs';
+    // Return undefined so that the load hook can determine the format
   }
 }